Download - Topic 7 : Nucleic Acids and Proteins
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Topic 7 : Nucleic Acids and Proteins
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7.1: DNA Structure and 7.2: DNA Replication
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7.1.1: Describe the structure of DNA, including the antiparallel strands, 3’–5’ linkages and
hydrogen bonding between purines and pyrimidines.
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IB Question: Outline the structure of part of a double stranded DNA molecule, using a simplifieddiagram. [5]
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IB Question: Outline the structure of part of a double stranded DNA molecule, using a simplifieddiagram. [5]N06/4/BIOLO/HP2/ENG/TZ0/XX
two strands of DNA;anti-parallel;3 to 5 linkages;′ ′purine / pyrimidine;A-T / G-C base pairing;hydrogen bonds;sugar-phosphate backbone; [5 max]Award [3 max] if answer does not include a diagram.
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IB question: Outline the structure of DNA. [5]
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IB question: Outline the structure of DNA. [5]
double helix;two chains of nucleotides / composed of nucleotides;nucleotides consist of base, deoxyribose (sugar)and phosphate;bases are adenine, cytosine, guanine and thymine;anti-parallel / strands;3 -5 links between nucleotides;′ ′hydrogen bonds between base pairs / purine and pyrimidine on opposite chains;only A-T and G-C / complementary base pairs are A-T and G-C ;two bonds between A-T and 3 between G-C; [5 max]Credit can be given for any of these points shown on a correctly drawn andlabelled diagram.
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7.1.1:Purines and pyrimidines
URACIL “U”
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7.1.2: Outline the structure of nucleosomes.7.1.3: STATE: Nucleosomes help to supercoil chromosomes and help to regulate transcription
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IB QUESTION: Outline the structure of nucleosomes. [2]
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IB QUESTION: Outline the structure of nucleosomes. [2]M09/4/BIOLO/HP2/ENG/TZ2/XX
(eight) histone (proteins); DNA wrapped around histones/nucleosome; further histone holding these together; [2 max] Do not allow histone wrapped around DNA.
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7.1.4: Distinguish between unique or single-copy genes and highly repetitive sequences in nuclear DNA.
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Single-copy genes Satellite DNA (highly repetitive sequences)
A single-copy gene has one locatable region on a DNA molecule.
Satellite DNA consists of highly repetitive sequences that can repeat up to 100,000 times in various places on a DNA molecule.
Single-copy genes make up 1–2% of the human genome.
Satellite DNA constitutes more than 5% - 45% of the human genome.
Single-copy genes are transcribed to make RNA, which in turn is translated to make a protein.
Satellite DNA is not transcribed, i.e .they do not code for protein.
A single-copy gene corresponds to a unit of inheritance (i.e., a protein).
Satellite DNA is not involved with inheritance.
Single-copy genes are usually thousands of base pairs in length. Satellite DNA is typically between 5 and 300 base pairs per repeat.
Single-copy genes are less useful for DNA profiling. Satellite DNA has a high rate of mutation making it useful for DNA profiling.
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IB QUESTION: Most of the DNA of a human cell is contained in the nucleus. Distinguish between unique and highly repetitive sequences in nuclear DNA. [5]
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IB QUESTION: Most of the DNA of a human cell is contained in the nucleus. Distinguish between unique and highly repetitive sequences in nuclear DNA. [5]
M10/4/BIOLO/HP2/ENG/TZ1/XX
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7.1.5 : STATE: Eukaryotic genes contain exons and introns
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7.2 D.N.A. Replication in prokaryotes7.2.1: State that DNA replication occurs in a 5’→ 3’ direction.
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7.2.2: Explain the process of DNA replication in prokaryotes, including the role ofenzymes (helicase, DNA polymerase, RNA primase and DNA ligase), Okazaki fragments and deoxynucleoside triphosphates.
Helicase
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RNA Primase
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RNA Primase
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DNA Polymerase III
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7.2.1 DNA replication occurs in a 5’ to 3’ direction.
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Nucleotides are added in the form of deoxyribonucleoside triphosphates
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DNA Polymerase I
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DNA Ligase
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Okazaki Fragments
Leading strand is synthesised continuously
Lagging strand is synthesised discontinuously
Complementary strands of DNA run anti-parallel to each other.
DNA pol III only synthesises DNA in a 5’ to 3’ direction
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IB QUESTION: Explain the process of DNA replication. [8]
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IB QUESTION: Explain the process of DNA replication. [8]
occurs during (S phase of ) interphase/in preparation for mitosis/cell division; DNA replication is semi-conservative; unwinding of double helix / separation of strands by helicase (at replication origin); hydrogen bonds between two strands are broken; each strand of parent DNA used as template for synthesis; synthesis continuous on leading strand but not continuous on lagging strand; leading to formation of Okazaki fragments (on lagging strand); synthesis occurs in direction; 5 3RNA primer synthesized on parent DNA using RNA primase; DNA polymerase III adds the nucleotides (to the end) 3 added according to complementary base pairing; adenine pairs with thymine and cytosine pairs with guanine; (Both pairings required. Do not accept letters alone.) DNA polymerase I removes the RNA primers and replaces them with DNA; DNA ligase joins Okazaki fragments; as deoxynucleoside triphosphate joins with growing DNA chain, two phosphates broken off releasing energy to form bond; [8 max] Accept any of the points above shown on an annotated diagram. (
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IB QUESTION: Explain prokaryotic DNA replication. [8]
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IB QUESTION: Explain prokaryotic DNA replication. [8]
DNA replication is semi-conservative / each strand of DNA acts as template; (DNA) helicase separates two strands/forms a replication fork; new strand built / nucleotides added in a to direction; 5 3 (deoxy)nucleoside triphosphates hydrolysed to provide energy for nucleotide formation/base pairing; on one strand DNA polymerase III builds continuous strand; on other strand short chains of DNA/Okazaki fragments are formed; each short chain starts with RNA primer; added by RNA primase; then remainder of chain of DNA built by DNA polymerase III; DNA polymerase I removes RNA primer and replaces it by DNA; DNA ligase joins DNA fragments together forming complete strand; replication only occurs at a single replication fork; [8 max] Award credit for any of the above points clearly drawn and accurately labelled.
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IB Question: State a role for each of four different named enzymes in DNA replication. [6]
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IB Question: State a role for each of four different named enzymes in DNA replication. [6]
Award [1] for any two of the following up to [2 max].helicase;
DNA polymerase / DNA polymerase III;RNA primase;DNA polymerase I;(DNA) ligase; 2 max
Award [1] for one function for each of the named enzymes.helicase:
splits / breaks hydrogen bonds / uncoils DNA / unwinds DNA;(DNA) polymerase III:
adds nucleotides (in 5' to 3' direction) / proof reads DNA;(RNA) primase:
synthesizes a short RNA primer (which is later removed) on DNA;(DNA) polymerase I:
replaces RNA primer with DNA;(DNA) ligase:
joins Okazaki fragments / fragments on lagging strand / makes sugar-phosphate bonds between fragments; 4 max[6]
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7.2.3. STATE: DNA replication is initiated at many points in a eukaryotic chromosome